Transcript Iperf Quick Mode Ajay Tirumala & Les Cottrell Iperf QUICK Mode  Problem – Current TCP apps cannot detect when they are out of slow-start  Bandwidth measurement.

Iperf Quick Mode
Ajay Tirumala & Les
Cottrell
Iperf QUICK Mode
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Problem
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Current TCP apps cannot detect when they are out of slow-start
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Bandwidth measurement apps have to run for a considerable time to
counter the effects of slow-start.
Plot from Brian Tierney, LBL
Sep 12, 2002
Iperf Quick Mode at LBL – Les Cottrell & Ajay Tirumala
Iperf Quick Mode at LBL – Les Cottrell & Ajay Tirumala
Sep 12, 2002
Iperf Quick Mode
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Solution
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Use Web100 to detect the end of slow-start
Measure bandwidth for a small period after slowstart (say 1s).
This should save about 90% of estimation time and traffic
generated.
Ideas evolved out of an email exchange between Tom
Dunigan, Brian Tierney & Les Cottrell
Iperf Quick Mode at LBL – Les Cottrell & Ajay Tirumala
Sep 12, 2002
Detecting end of Slow-start
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Outline
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Determine a sampling period for Congestion Window
Detect the absence of exponential increase every RTT
Handle pathological cases
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Connection may not get out of slow-start
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Connection may have a very small bandwidth-delay product.
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Multiple slow-starts
E.g. localhost transfers, with latency in nano-seconds.
At present, it handles Reno and Vegas
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It should handle Net100/Floyd stacks with minor modifications.
Iperf Quick Mode at LBL – Les Cottrell & Ajay Tirumala
Sep 12, 2002
The Quick mode Algorithm
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Initialize Iperf sockets and initialize Web100 connection
for the for the Iperf socket.
Start Web100 data collection thread
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Detect the end of slow-start in the data transfer thread
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This will indicate when the connection is definitely out of slowstart
If congestion window does not stabilize, do NOT report QUICK
mode results
Measure bandwidth for 1s (or user specified time) after
slow-start
Only client requires Web100, can use unmodified iperf
server
Iperf Quick Mode at LBL – Les Cottrell & Ajay Tirumala
Sep 12, 2002
SLAC – CERN, 160ms
Note 2 slow starts, 4 secs to
reach stability
Results
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Slow-starts can be
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From 0.2 seconds
for low-latency
networks
Up to 5 sec for long
haul high bandwidth
networks.
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Maximum gains
here by using
Iperf in QUICK
mode.
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Unless, we use it
in quick mode,
we can never be
sure that the
connection is out
of slow-start
Performed tests on dialup links (as receiver) through
hundreds of Mbits/s links with over 150ms RTT
Iperf Quick Mode at LBL – Les Cottrell & Ajay Tirumala
Sep 12, 2002
Results
SLAC-Japan
140ms * 350Mbits/s ~
6MByte)
SLAC-TRIUMF
RTT 72 ms.
congested link
Iperf Quick Mode at LBL – Les Cottrell & Ajay Tirumala
Sep 12, 2002
Results
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Differs with throughputs for running iperf for 20s
by less than 10%
Traffic
reduction
92%
Measure
ment time
reduced
by 94%
Iperf Quick Mode at LBL – Les Cottrell & Ajay Tirumala
Sep 12, 2002
Web100 experiences
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A must use tool (We are fans)
User-APIs can be improved
Behaves well for a sampling time of 20ms.
Iperf Quick Mode at LBL – Les Cottrell & Ajay Tirumala
Sep 12, 2002
Possible areas to investigate
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Integrate with BW tests.
Perform tests with slow-senders (e.g. dialup).
Empirical estimates immediately after slow-start :
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Using RTT and rate of increase of congestion window.
Iperf Quick Mode at LBL – Les Cottrell & Ajay Tirumala
Sep 12, 2002
Links
Iperf Quick mode :
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http://www-iepm.slac.stanford.edu/bw/iperf_res.html
Documentation and results of tests with all IEPM-BW managed
nodes available from this link.
Iperf Quick Mode at LBL – Les Cottrell & Ajay Tirumala
Sep 12, 2002
Other stuff…
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Miniperf is a small Iperf-like program written to
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Monitor user-specified Web100 variable(s)
Allows setting window sizes and test times
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Can include parallel thread functionality
Generate graphs (rate based, sum based)
Generate HTML
Created a single Iperf version to run on IPv4/v6
(Web100)/(no Web1000).
Iperf Quick Mode at LBL – Les Cottrell & Ajay Tirumala
Sep 12, 2002
Thank you!!!